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As the summer heats up, it’s worth taking a look back in the year when cannabis research was just as hot. Exciting new studies continue to come out with the global trend toward legalization and acknowledging the therapeutic potential of cannabis.

Research so far this year encompasses finding the region in the brain that gets you high to the medicinal benefits of CBD. Below are some stand-out research papers from the first half of the year.

States With Liberal Cannabis Policies Have Lower Rates of Cannabis Use Disorders

Opponents of cannabis legalization claim that increasing access will increase problematic cannabis use. However, that idea is based more on gut feelings than scientific evidence.

Public health scientists put it to the test by comparing state-level policy liberalism rankings over the last couple decades with data collected regarding cannabis use and rates of cannabis use disorder. Notably, this assessment was limited to medical cannabis legalization and didn’t incorporate data relating to the legal recreational market now available in many states.

Overall, more people used cannabis in states with liberal cannabis policies than conservative-policy states, but the prevalence of cannabis use disorders was highest in conservative-policy states.

It’s uncertain at this point why conservative policy states would have higher cannabis use disorder rates, but it suggests that strict restriction of access to cannabis is not the solution to eliminating problematic use, and instead, increasing access may lead to safer overall use.

Looking for the Brain Region That Causes the High

People have been experiencing cannabis highs for thousands of years. Only recently, however, have scientists uncovered how this effect occurs in the brain.

THC was isolated in the 1960s and the CB1 receptor wasn’t fully discovered until the 1990s. Shortly after, it was confirmed that activation of CB1 receptors by THC causes the feeling of being high. However, where in the brain this feeling comes from remained elusive.

Discovering the seat of the high was likely not the scientist’s intention. Instead, they were looking at the brain activity of participants given either 8 mg of THC alone or THC with 10 mg of CBD. They revealed that THC disrupted activity in numerous brain regions, but the posterior cingulate cortex was specifically disrupted by THC alone, and less-so by THC with CBD.

Importantly, the degree of disruption positively correlated to the feeling of being stoned and high. So while THC’s actions across many brain regions are responsible for the numerous outcomes of using cannabis (e.g., memory, munchies, mood), your high can be traced to the posterior cingulate cortex.

So where is the posterior cingulate cortex? If you were to split the brain right down the middle, front to back, you’d slice through a large band of fibers called the corpus callosum that allows the two sides of the brain to communicate with one another. The brain’s outer layer that sits right above the corpus callosum on each side of the brain is the cingulate cortex, and the posterior end is the part toward the back of your head.

Numerous studies have investigated whether cannabis use during adolescence changes the way the brain looks. However, these studies are often limited by a small sample size or only compare frequent consumers who consume more than three times per week. Few studies have looked at structural brain differences across different levels of cannabis consumption.

In this study, the brains of 781 adolescents aged 14-22 were compared. 109 participants were classified as occasional cannabis consumers (two or fewer uses per week) and 38 were classified as frequent consumers.

The Philadelphia-based scientists used brain MRIs to look at structural differences on a brain-wide and region-specific level. They concluded that neither occasional nor frequent cannabis use significantly affected the size of the whole brain or any of the specific regions of interest.

Further, there were no group differences in the number of brain cells, their connections, or in the thickness of the cortex—the surface of the brain that contributes to the unique cognitive abilities of humans and higher-order species.

While these findings suggest that adolescent cannabis consumption doesn’t affect the way the brain looks, it doesn’t address questions relating to the effect of cannabis on the way the brain functions. Nonetheless, this study serves as further support for the less-damaging effects of cannabis use compared to other drugs (such as alcohol), which have been shown to affect brain structure.

CBD Protects Against THC’s Effects on Learning and Memory

It turns out that CBD blocks some of the effects of THC, and it has become clear that the underlying reasons extend beyond just CBD’s actions on CB1 receptors. Since THC itself has numerous therapeutic benefits, understanding how CBD blocks some of THC’s negative effects, such as impairing learning and memory, could elevate the utility of THC-based therapies.

A collaborative effort of scientists across Spain and Japan revealed that CBD can block THC’s activating effects on CB1 receptors indirectly by increasing the activation of another type of receptor, the adenosine type IIa receptor. The adenosine receptor appears to oppose the actions of CB1 receptors—when the adenosine receptor is active, the CB1 receptor is not. By increasing adenosine activation, CBD can therefore block THC’s effects.

Intriguingly, this mechanism only influenced THC’s actions in the hippocampus region of the brain, which plays a critical role in laying down long-term memories. As one can predict, CBD prevented THC’s impairing effects on new memory formation.

Narrowing Down the Culprit of Cannabinoid Hyperemesis Syndrome

Cannabinoid hyperemesis syndrome (CHS) is a somewhat newly recognized condition that is characterized by cycles of severe stomach cramping and vomiting in frequent cannabis consumers. The number of cases is on the rise and while there is no confirmed cause, increasing THC potency in average recreational strains has usually been deemed the culprit.

To address whether high levels of THC are responsible for CHS, cannabinoid content in hair samples was analyzed from patients with CHS admitted to emergency departments in Ontario, Canada, and compared with two other groups: patients admitted to the emergency department for an unrelated condition, and recreational cannabis consumers without CHS.

The results revealed that THC levels were similar across the three groups, ruling out the possibility that CHS arises due to high levels of THC in the body. Intriguingly, the THC:CBN ratio was 2.6 times lower in the CHS group than in the recreational consumers without CHS, suggesting a potential protective role of additional cannabinoids.

If THC is not the sole cause of CHS, then what is? There are at least two remaining hypotheses. The first is that some patients experience a build-up of toxins, such as pesticides and molds, from repeated consumption, which triggers the body’s emetic response (i.e., vomiting) through activation of certain cells in the brainstem.

The second is that THC weakens the action of certain CB1 receptors in some people more than others. It turns out that activating CB1 receptors (as THC does) in the brain has anti-emetic effects—which explains THC’s well-known anti-nausea effect.

But it’s believed that CB1 receptors in the brain are more prone to weakening than those in the gut—therefore, heavy THC use in some people could lead to a weakening of the anti-emetic actions in the brain while leaving the pro-emetic actions in the gut unaffected. The result may be hyperemesis.

CBD Could Effectively Treat Related Symptoms of Autism

There is plenty of anecdotal support for cannabis-based therapies in Autism Spectrum Disorder (ASD), but those claims have lacked clinical support until now. ASD is characterized by core deficits in social, communication, and motor behaviors.

While these symptoms present their own challenges, comorbid symptoms such as self-injurious behavior, hyperactivity, anxiety, and sleep disorders are especially burdensome to the patient and their caregivers. Children with ASD are often on several medications to help relieve these comorbid symptoms, and not always successfully. Given CBD’s therapeutic range, it represents a single treatment strategy for combating these comorbid symptoms in ASD.

The effect of a 20:1 CBD:THC oil was assessed on comorbid ASD symptoms in 53 children between the ages of 4 and 22 years of age. Parents were free to administer as much of the oil as they wanted (recommended daily dose was 16 mg CBD per kilogram of body weight), but children ended up consuming around 90 mg of CBD each day.

Despite consuming less than the recommended amount, CBD reduced hyperactivity, lowered the number of self-injurious behaviors, improved sleep, and reduced anxiety in a majority of patients.

An overall improvement in at least one of the comorbid symptoms was observed in 75% of the participants and only worsened overall symptoms in 4%. Although CBD didn’t improve any one of the symptoms better than conventional treatments, it represents a single pharmaceutical approach that can target a myriad of symptoms simultaneously with limited adverse events.

Josh Kaplan, Ph.D., is an Assistant Professor of Behavioral Neuroscience at Western Washington University. He is a passionate science writer, educator, and runs a laboratory that researches cannabis' developmental and therapeutic effects.

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Juanita Leatham

Hi, when you say, “It’s uncertain at this point why conservative policy states would have higher cannabis use disorder rates” – do you think that the way the conservative policy states define a cannabis use disorder could be why the rates are so high? Are the people who use cannabis (small doses, infrequent) in these conservative policy states put into a category of use disorder solely because they use cannabis (further perpetuating the “bad drug” mentality that keeps conservative policy in place)? I’m interested in your take on this.

Josh

It’s an interesting thought, Juanita, but cannabis use disorder is clinically-defined so it’s diagnosis should be the same across states, regardless of their political leaning or cannabis legalization policies.

Amber Byrd

A symptom of cannabis use disorder is taking cannabis in high risk situations. Perhaps this is a form of self harm, as they could potentially get in trouble or maybe they get another kind of “high” from getting away with doing something that’s illegal. If cannabis is illegal in their state, any form of using cannabis is high risk so they have more opportunities to satisfy the urge to use in a high risk situation. So maybe this high risk use is key to developing cannabis use disorder?